feat(PBR): extract Blender PBR properties and apply in 3D viewer

Extract Base Color, Metallic, Roughness, Transmission, IOR from Blender
asset library materials via catalog_assets.py. Store in catalog JSON and
serve via /api/asset-libraries/pbr-map endpoint. Frontend viewers apply
PBR properties to Three.js MeshStandardMaterial using hex color strings
(avoiding Three.js ColorManagement sRGB/linear issues).

Key fixes:
- RLS bypass for material alias lookup in pbr-map endpoint
- pbrMap empty guard prevents premature grey fallback in viewers
- Cache-Control: no-cache on pbr-map requests to avoid stale data

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/pages/AssetLibrary.tsx

@@ -241,14 +241,17 @@ function LibraryCard({ lib }: { lib: AssetLibrary }) {
           </button>
           {expanded && (
             <div className="mt-2 flex flex-wrap gap-1">
-              {lib.catalog.materials.slice(0, MAX_VISIBLE).map((m) => (
-                <span
-                  key={m}
-                  className="text-xs px-2 py-0.5 rounded bg-surface-alt border border-border-default text-content-secondary font-mono"
-                >
-                  {m}
-                </span>
-              ))}
+              {lib.catalog.materials.slice(0, MAX_VISIBLE).map((m) => {
+                const name = typeof m === 'string' ? m : m.name
+                return (
+                  <span
+                    key={name}
+                    className="text-xs px-2 py-0.5 rounded bg-surface-alt border border-border-default text-content-secondary font-mono"
+                  >
+                    {name}
+                  </span>
+                )
+              })}
               {materialCount > MAX_VISIBLE && (
                 <span className="text-xs px-2 py-0.5 rounded bg-surface-muted text-content-muted">
                   ... and {materialCount - MAX_VISIBLE} more